Machine tool

ABSTRACT

A machine tool having a table which is slidable on ways and which is driven by a torque motor; a stop is provided to terminate table movement, which stop is relatively flexible and is provided with a strain gage; a computer is used for controlling the torque on the motor and changing from one torque to another at various positions in table travel.

United States Patent [1 1 Wake [451 Jan. 9, 1973 54 MACHINE TOQL3,220,286 11/1965 Jacobson et al. ..408/l2 [75] Inventor: John A. Wake,Auburn, Mass. Primary Examiner Gil weidenfeld [73] Assignee: CincinnatiMilacron-Heald Corp., Attarney--Norman S, Blodgett Worcester, Mass.

22 Filed: June 16, 1971 ABSTRACT [2!] Appl. No.: 153,702 A machine toolhaving a table which is slidable on ways and which is driven by a torquemotor; a stop is provided to terminate table movement, which stop is5.81 4084;215:2315; relatively flexible and is provided with a Strain gg a [58] Field Qr s Q r QIQ lib'/i'i"i'6" 14 6 12' wmPuter is used 5 5 5motor and changing from one torque to another at various positions intable travel.

[56] References Clted 5 Claims, 6 Drawing Figures UNITED STATES PATENTS3,244,029 4/1966 Jacobson ..408/l0 PATENTEDJAH 9 ma 3. 709,821

SHEET 1 OF 3 I I I II FIGZ I.

NVENTOR. JOHN A; WAKE BY 110m iWW ATTORNEY PATENTED JAN 9 I975 SHEET 2[IF 3 PAIENIEU M' 9 I973 3,709,621

SPEED- LOAD Q, I60 VOLTS 4000 I60 I600 HMS AMPERES 2000 so 800-\QCONITORQUE SAFE OPERATING \tys. SPEED ZONE-(LIMIT) CONNECTION DIAGRAMCSQ' 54 FOR NC CONTROL MOTORS POWER TB2 TB! CONNECTIONS ,A 1 V3 7 1 I 0l8 9 55 DC 0 l 8 24w: 2 AMP T l6 7 AVAIL BLEFOR A 0 l5 s O }EXTERNALDRIVE 0 l4 5 6-- CONTROL RELAYS MQTOR O 4 i .2 i2 1 3 i O n 2 +3 1 5sPOSITlON O I I FEED 1 525 -99P. i

FIG.6

MACHINE TOOL BACKGROUND OF THE INVENTION In the design of machine tools,there are many situations where a table carrying a tool is moved over aset of ways with a programmed speed and displacement. In a way-typemachine tool, a large number of such tables on ways may be provided. Ithas been the practice in the past to operate these table movementstoward and away from a workpiece moving from station to station along amain way of the machine by using hydraulic cylinders. In order toprovide even the simplest type of table movement, a considerable numberof hydraulic valves, conduits, and electrical switches must be provided,as well as a source of hydraulic fluid. This means that there is a largenumber of pumps, sumps, flexible conduits, and the like located aroundthe normal machine parts, so that even a relatively simple way-typemachine tool has an awkward appearance, is difficult to keep clean, andpresents certain dangers to the personnel working around it.Furthermore, in order to change the way-type machine operation for adifferent workpiece, it is necessary to change switches and valves, andto use different size orifices in the hydraulic circuitry to produce adifferent set of feeds and speeds. Attempts to provide such a machinefor general purpose, thus permitting rapid changes from one workpiece toanother, have resulted in very complicated and expensive apparatus aswell as a system which is quite unreliable. Furthermore, many suchmachines include a terminating stop point in the table movement to allowthe tool to make a bottoming lateral surface cut; the repeatability oflocation of such a surface has always been very poor. These and otherdifficulties experienced with the prior art devices have been obviatedin a novel manner by the present invention.

It is, therefore, an outstanding object ofthe invention to provide amachine tool having an electrically-driven table which is capable ofgood repeatability at a stop position.

Another object of this invention is the provision of a machine tool,particularly for use in a multi-station transfer line, which is free ofall of the accessories necessary for hydraulic operation.

A further object of the present invention is the provision of a machinetool having accurate control of force between the tool and the workpieceand capable of easy change or adjustment of torque, speed, and distancein the machine tool cycle.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION In general, the present invention has to dowith a machine tool having a base and a tool-carrying table slidablymounted on the base. A screw-and-nut drive meansjoins the table to thebase to bring about relative slidable movement between them and a motoris connected to the drive means for the operation thereof. The motor hasthe characteristic of substantially constant torque irrespective ofspeed. A stop is mounted on the base and engageable by the table at apredetermined part of the said relative movement, the stop including astrain gage giving a signal proportional to the force on the stop.

More specifically, the motor is connected to a control means including acomputer for regulating the torque and speed thereof, and the straingage is connected to the control means to shift the operation of themotor to a low torque level when the stop deflection reaches apredetermined level.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention,however, may be best understood by reference to one of its structuralforms, as illustrated by the accompanying drawings, in which:

FIG. 1 is a perspective view of a machine tool incorporating theprinciples of the present invention,

FIG. 2 is a side view of a portion of the machine tool taken on the lineIIlI of FIG. 1,

FIG. 3 is a perspective view of the portion of the machine tool shown inFIG. 2,

FIG. 4 is a vertical sectional view of a portion of the machine tooltaken on the line IVIV of FIG. 3,

FIG. 5 is a graph showing various characteristics ofa motor forming partof the invention, and

FIG. 6 is a diagrammatic view of the control means for the machine tool.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, whichbest shows the general features of the invention, the machine tool,indicated generally by the reference numeral 10, is shown as having abase 11 including an elongated way 12 on which is mounted a transfertable 13 and on which is, in turn, mounted a workpiece l4. Arrangedaround the way 12 is a plurality of machining units l5, l6, 17, I8, 19,and 21 which are connected to a control means 22 by cables 23, 24, 25,26, 27, and 28, respectively. Control means 22 includes a computercapable of being programmed for various types of workpieces 14 toregulate the operation of the various machining units.

In FIG. 2 it can be seen that the machining unit 15 consists of a table29 slidable on ways 31 and extending at a right angle to the ways 12associated with the transfer table 13. An adjustable dog 32 on the tableis in position successively to engage switches 33 mounted on the side ofthe base 11. Also mounted on the base 11 is a motor 33 for bringingabout movement of the table 29 relative to the base 11. Mounted on theupper surface ofthe table 29 is a toolhead 34 from which extends aspindle 35 having at one end a cutting tool 36. An electric motor 37 isconnected to the toolhead for driving the spindle 35.

In FIG. 3, it can be seen that the motor 33 is mounted on a slab 38extending across the base 11 between the ways 31. The cable 23 extendsdownwardly from the motor 33.

The sectional view shown in FIG. 4 illustrates how the table 29 isprovided with a nut 41 which is threadedly engaged by a screw 42. Thescrew extends through a roller bearing 43 which is protected by suitableseals 44. Screw 42 extends through the slab 38 and is directly connectedto the shaft of the motor 33. It can be seen that the outboard end ofthe motor 33 is provided with a tachometer generator 55. The signalextends to the computer 54 by means of the cable 56.

At the other end of the base 11 from the motor 33 is a shelf 45 on theupper horizontal surface of which is mounted a stop 46. The stop isadjustable longitudinally of the table, i.e., in a direction parallel tothe ways 31 by a slot-and-bolt connection. The stop is provided with anupstanding finger 47. This finger is cantilever-supported and is in aposition to be engaged by an abutment 48 extending downwardly from theunderside of the table 29. On the surface of the finger 47 is fastened astrain gage 49 which is connected by a cable 51 to an analyzer andamplifier circuit 52 whose output is connected through a cable 53 to thecontrol means 22. The finger 47, the strain gage 49, and the circuit 52are shown and described in detail in the patent of Jacobson No.3,244,029, which issued on Apr. 5, 1966. Leaving the circuit 52 by wayof the cable 53 is an electrical signal whose magnitude is in directproportion to the amount of deflection of the finger 47 in response topressure on it from the abutment 48.

Referring to FIG. 5, the graph shows the various characteristics of themotor 33. The motor is of the type known as a torque motor, such as thedirectdrive DC motor-tachometer manufactured and sold by inland MotorCorporation Of Virginia, known as the TT-5746 motor. In the preferredembodiment, this motor can provide continuous torque of 17 pound-feetwith a peak torque of 85 pound-feet. It is a totally enclosed,non-ventilated motor. As such, this continuousduty, direct-drivecombination DC torque motortachometer generator provides a hightorque-to-inertia ratio. It is provided with DC current from a 100 watttransistorized drive system 53 (see FIG. 6) contained in the controlmeans 22 which also contains a computer 54.

The operation of the machine tool 10 will now be readily understood inview of the above description. The workpiece 14 is moved with the table13 along the ways 12, so that it comes into operative relationship tothe various stations or machining units l5, l6, 17, 18, 19, and 21.These machining units are all similar to the unit 15 which has beendescribed above in detail. Each of the machining units is provided withthe motor similar to the motor 33 of the unit 15 and the stop 46, aswell as the switches 33. The computer 54 of the control means 22regulates the operation of all of these machining units in sequence (andat times together) on the workpiece. Referring particularly to FIG. 4,it can be seen that the motor 33, by rotating the screw 42, causes thenut 41 and the table 29 to move to the left. At various times in itsmovement, the tool 36 will come in contact with portions of theworkpiece 14 to perform various operations. During the longitudinalmovement of the table 29, the dog 32 engages the switches 33 to set updifferent motor conditions for rotation of the spindle 35 and theadvancement of the table under the impetus of the motor 33. Eventually,the table 29 reaches the stop 46 and is engaged therewith through themedium of the abutment 48. At the time of engagement, the motor 33 isproviding the table drive means with a torque of high value. When theabutment 48 engages the finger 47, this torque continues to operate tobend the finger 47. From the curve in FIG. 5, it can be seen that thetorque, even at zero speeds, is almost the same as at substantialspeeds, so that the stalling of the motor does not cut off torque orforce pressure against the finger 47. The signal leaving the strain gage49 and its circuit 52 rises as the deflection of the finger takes placeat a predetermined voltage or deflection of the finger. The controlmeans indicates a change in torque required from the motor 33. Thetorque in the motor 33 is reduced substantially, so that the table 29comes to a stop with a given deflection of the finger 47 and the torquefrom the motor presses the table against the finger with a fixed torqueand force. The tool 36 is used for a suitable operation, such as forminga radial surface on a flange or bottoming out a bore; the radial surfacethus formed is repeatable from workpiece to workpiece with extremeaccuracy because of the construction and operation described above.

It can be seen that the present invention results in a machine toolwhich is not surrounded by various hydraulic equipment, such as valves,sumps, pumps, flexible conduits, and the like which are not onlydangerous to the operator but are also aesthetically unpleasing. Becauseof the electrical characteristics of the apparatus, it is possible touse a digital computer 54 to regulate the entire operation, includingthe operations of the individual machining units.

The tachometer generator 55 issues digital pulses responsive to anangular increment of rotation of the motor 33, so that the issuance ofpulses corresponds to the number of revolutions. The position of thetable 29 is also indicated by means of a counter contained in thecomputer. Fundamentally, the switches 33 are actuated during the motionof the table and act through potentiometers of selected value into thelines leading to the drive system. This causes a different DC current topass to the motor 33 and thus adjust the torque. The table with itsabutment 46 is pressed against the stop 46 for a given length of time,usually the length of time necessary to perform the machining operationat that particular point. Because of the flexibility of the computer, itis only necessary to change programming to operate with a differentworkpiece 14. Furthermore, with a given type of workpiece, it ispossible, if the surface finish deteriorates, for instance, to changethe feed, speed, and so on of the machine to correct such a deficiencyin the finished workpieces.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. it is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:

1. A machine tool, comprising a. a base member,

b. a table member adapted to carry a tool and slidably mounted on thebase,

. a drive means joining the table member to the base member to bringabout relative slidable movement between them,

. a motor drivingly connected to the drive means for the operationthereof, the motor having the characteristic of substantially constanttorque irrespective of speed, and

e. an abutment on one of said members engagable with a stop of the otherof said members at a predetermined part of the said relative movement,

the stop including a strain gage giving a signal proportional to theforce on the stop, and

f. control means associated with said motor and said strain gage toregulate the torque level of the motor in response to the deflection ofsaid stop.

2. A machine tool as recited in claim 1, wherein the motor is connectedto said control means and said control means includes a computer forregulating the torque level.

3. A machine tool as recited in claim 2, wherein a plurality of limitswitches are located along the base member to be operated sequentiallyby the table member during the said relative movement, and wherein theswitches are connected to the control means to bring about changes inthe operation of the motor.

1. A machine tool, comprising a. a base member, b. a table memberadapted to carry a tool and slidably mounted on the base, c. a drivemeans joining the table member to the base member to bring aboutrelative slidable movement between them, d. a motor drivingly connectedto the drive means for the operation thereof, the motor having thecharacteristic of substantially constant torque irrespective of speed,and e. an abutment on one of said members engagable with a stop of theother of said members at a predetermined part of the said relativemovement, the stop including a strain gage giving a signal proportionalto the force on the stop, and f. control means associated with saidmotor and said strain gage to regulate the torque level of the motor inresponse to the deflection of said stop.
 2. A machine tool as recited inclaim 1, wherein the motor is connected to said control means and saidcontrol means includes a computer for regulating the torque level.
 3. Amachine tool as recited in claim 2, wherein a plurality of limitswitches are located along the base member to be operated sequentiallyby the table member during the said relative movement, and wherein theswitches are connected to the control means to bring about changes inthe operation of the motor.
 4. A machine tool as recited in claim 2,wherein the strain gage is connected to the control means to shift theoperation of the motor to a low torque level when the stop deflectionreaches a predetermined level.
 5. A machine tool as recited in claim 1,wherein the drive means is of the screw-and-nut type, and wherein thestop is mounted on the base member for engagement by the table member.